Aakash Ganga (AG) is one of the signature innovations that Dr. BP Agrawal developed under Sustainable Innovations (SI), a non-profit organization. SI harvests innovations in systems, technologies and entrepreneurship to build holistically sustainable social enterprises. AG is a rainwater harvesting system utilized to collect safe drinking water in the arid region of Rajasthan, India. The system channels rooftop rainwater from every house in a community through gutters and pipes to a network of multi-tier underground reservoirs with large enough capacity to store a year of drinking water.

Part of the harvested rooftop rainwater is stored in the House Tank, or Griha Tanka, a reservoir attached to a house for the exclusive use of the home owner. Typically, the Griha Tanka stores enough water to meet the drinking water needs of the family for a year.

The rest of the rainwater flows to the Community Tank, or Gram Tanka, a shared community reservoir. People who live under thatched roofs or who cannot afford to have their own reservoirs take water from the shared reservoir.